Luminous electronic display devices include electroluminescent displays (hereinafter referred to as “ELDs”). Components of ELDs include an inorganic electroluminescent element and an organic electroluminescent element (hereinafter referred to as “organic EL element”). An inorganic electroluminescent element, which is used as a planar light source, requires a high AC voltage for driving the luminous element.
An organic EL element includes an anode, a cathode, and a luminous layer containing a luminous compound and disposed between the anode and the cathode, and emits light (fluorescence or phosphorescence) through deactivation of excitons generated by recombination of electrons and holes injected into the luminous layer. The organic EL element, which is of a self-luminous type, can emit light at a low voltage of about several volts to several tens of volts, and has a wide viewing angle and high visibility. The organic EL element, which is a thin, completely solid element, has received attention in terms of, for example, space saving or portability. Attempts have been made to produce a flexible organic EL element by replacing a rigid substrate with a flexible plastic or metal foil substrate, so that the organic EL element of a completely solid type can be more effectively utilized.
Organic EL elements are also characterized as being planar light sources, unlike primary light sources which have been put into practice, such as light-emitting diodes and cold-cathode tubes. Organic EL elements are applied to light sources for illumination and backlight units of various displays, which effectively utilize the characteristics of the organic EL elements. In particular, organic EL elements are suitable for use in backlight units of full-color liquid crystal displays, which have been increasingly demanded.
In contrast to a conventional EL element which emits only light of a single color, Patent Literature 1 discloses an organic EL element including a luminous layer having regions which are intentionally deprived of emission function through irradiation with UV rays, a laser beam, or an electron beam (i.e., formation of non-emission regions on the luminous layer), the organic EL element being capable of forming emission patterns corresponding to the non-emission regions during emission of light (see paragraphs [0026] and and Example 1).
Although Patent Literature 1 discloses a technique for formation of emission patterns during emission of light, the literature does not refer to creation of values of the organic EL element during non-emission of light.